1. Field of the Invention
The present invention relates generally to electric discharge machines (EDM) and more particularly to an electrode tube holding apparatus for an EDM.
2. Description of the Related Art
A general EDM works like that a rotatable chuck mounted to a spindle thereof holds and drives an electrode tube to rotate and eject high-pressure machining liquid and then electro-discharge machining is applied to a workpiece after the electrode tube is electrified, whereby a deep hole is formed in the workpiece for the machining purpose. Referring to FIGS. 1-2, the electrode tube 1 of the conventional EDM is held at the rotatable chuck 2 and at a die guide 4 of a die guide holder 3 below the spindle 5. As shown in FIG. 2, while the electro-discharge machining proceeds, some deviations will occur between the axis of the rotatable chuck 2 and the axis of the electrode tube 1 and such deviations will result in deformation of the electrode tube 1 due to centrifugal effect while the electrode tube 1 is rotated. Although the electrode tube 1 is held by the die guide 4, the length of the electrode tube 1 causes the centrifugal effect on itself to incur excursion of its distal end, which has become a serious problem. When such excursion is slight, some problems may happen, like deviation of the hole or enlarged diameter of the hole after machining. When such excursion is serious, it may even disable the EDM from normal operation. In this way, the conventional EDM is too unstable to apply the electro-discharge machining to the microminiature hole.